Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$150.39	3.227%	$155.2431	$155.24	$155.25	$155.20
Purchase #2	$215.65	13.435%	$244.6226	$244.62	$244.60	$244.60
Purchase #3	$215.52	11.337%	$239.9535	$239.95	$239.95	$240.00
Purchase #4	$48.92	11.482%	$54.537	$54.54	$54.55	$54.50
Purchase #5	$142.54	4.159%	$148.4682	$148.47	$148.45	$148.50
Purchase #6	$88.54	11.591%	$98.8027	$98.80	$98.80	$98.80
Purchase #7	$187.39	4.819%	$196.4203	$196.42	$196.40	$196.40
7 purchase totals =	$1,048.95		$1,138.0474	$1,138.04	$1,138.00	$1,138.00